208 Morphology and Systematic Botany under [BOOKI. 



Chara, though without understanding them. Observations on 

 conjugating Algae were multiplied; Ehrenberg in 1834 saw 

 corresponding phenomena in Closterium, and Morren described 

 them more exactly in 1836. The formation of swarmspores in 

 fresh-water and salt-water Algae was frequently observed 

 between 1820 and 1830, and in his ' Neues System,' iii, which 

 appeared in 1839, Meyen gave a summary of all that was 

 known up to that time of the propagation of the Algae. But 

 a new aspect was given to the knowledge of the Algae by those 

 researches of Nageli between the years 1844 and 1849, which 

 have been already mentioned, and which are the first since 

 Vaucher's time that can be regarded as systematic. Nageli 

 studied especially the laws of cell-division in sexual multiplica- 

 tion and growth, but he considered the Florideae to be the 

 only Algae that were sexually differentiated, and distinguished 

 the rest as being without sexuality. Braun in his ' Verjiingung' 

 (1850) made numerous contributions to the biology of the 

 fresh-water Algae, affording many and most interesting glimpses 

 into a connection still little understood between these forms ; 

 and in 1852 he gave an account of the history of growth in the 

 Characeae, a work conceived in Nageli's spirit and a model of 

 scientific research, in which the mode of derivation of every 

 cell from the apical cell of the stem was shown, the sexual 

 organs were minutely examined, and the relation established 

 between the direction of the * streaming ' of the cell-contents 

 and the morphology of the organs. Gustav Thuret had already 

 made the zoospores of the Algae the subject of detailed exam- 

 ination. 



Such was the condition of affairs with respect to the Algae 

 about the year 1850, when Hofmeister made the formation of 

 the embryo in the Phanerogams, the Vascular Cryptogams, 

 and the Muscineae the central point of investigation in 

 morphology and systematic botany. He made it clear that 

 a perfect insight into the whole cycle of development in the 

 plant and into its affinities can only be obtained, if we succeed 



